Mostly from some nozzles with leaded brass components, but lead is probably very small component and I'm not sure is the main reason why something printed isn't food safe. Mostly I think it's not food safe because it's not really a traceable chain, has very high surface areas, lots of bacterial pockets, generally hard to determine if it's food safe or not.
But wrt to lead, it would mostly be in brass components
But wrt to lead, it would mostly be in brass components